Start by measuring the all-purpose flour, sugar, instant yeast, kosher salt, and lemon zest into the bowl of a stand mixer. Stir these dry ingredients together until well combined. This initial mixing ensures that the yeast and salt are evenly distributed throughout the flour, which is crucial for a successful rise.
Next, add the milk, egg yolks, unsalted butter, and pure vanilla extract to the dry mixture. Attach the dough hook to your stand mixer and knead the dough on medium speed for about 10 minutes. You'll know it's ready when the dough is soft, supple, and no longer sticky to your fingers. If it feels too sticky, feel free to add a bit more flour.
Once the dough is kneaded, shape it into a ball and lightly spray the mixing bowl with some oil. Place the dough ball back in the bowl, cover it loosely with plastic wrap, and allow it to rise in a warm place for 45 to 60 minutes, or until it has doubled in size. This resting period is essential for developing the gluten structure and gives the Berliner their fluffy texture.
After the dough has risen, gently punch it down in the center to release the air. Turn it out onto a floured surface and divide it into equal pieces. I recommend weighing the dough pieces to about 80 grams each if you want to get precisely 15 Berliner. Each piece should be uniform for even cooking.
Roll each piece into a smooth ball using the palms of your hands. Place them on a lined baking sheet, ensuring there’s space between each for rising. Once formed, cover the dough balls with a clean towel or loosely with plastic wrap and let them rise for another 30 to 60 minutes until they are puffy and nearly doubled.
While the dough is rising, prepare your frying oil. In a deep pan, heat enough oil to have at least 2 inches deep. Keep the oil temperature between 350 and 365 degrees Fahrenheit. If the oil is too cool, the Berliner will soak up the oil and become greasy. A thermometer can be super helpful here!
Once the oil is hot, carefully drop a few of the dough balls into the oil, being cautious not to overcrowd the pan. Fry them for about 2 minutes on one side, or until golden brown, then flip them to cook the other side for another 2 minutes. It’s important to keep an eye on the temperature, as uneven frying can lead to burnt outsides and raw insides.
After frying, remove each Berliner and place them on paper towels to drain any excess oil. Allow them to cool slightly before filling. Repeat the frying process for the remaining dough balls.
When they are cool enough to handle, it’s time to fill the Berliner. Use a piping bag fitted with a filling tip and fill each donut with your choice of raspberry jam. Insert the tip into the side of the donut, and squeeze gently to fill.
For the finishing touch, mix granulated sugar with a pinch of cinnamon in a shallow bowl. Roll each filled Berliner in the sugar mixture until well coated. Finally, dust the tops with powdered sugar for that classic look. Serve them warm for an unforgettable treat!